In the manufacture of paper, the paper web is passed through a dryer section, after the forming and press sections, to further remove entrained water and to correspondingly increase the density of paper fibers. In the dryer section, the wet paper web is passed about and held in contact with upper and lower arrays of heated cylinders to remove water in the web. The paper web is held in thermal contact with the heated cylinder by a dryer felt or dryer fabric, generally called a dryer fabric, which is in the form of an endless belt. Dryer fabrics in modern papermaking machines may have a width of from 5 to over 32 feet, a length of from 40 to over 400 feet and weigh approximately 100 to over 3,000 pounds. These fabrics wear out and may require replacement after only 8 months of continuous operation. At the present time, replacement of dryer fabrics now involves taking the machine out of service, removing the worn fabric, setting up to install a new fabric and installing the new fabric. Installation of the new dryer fabric includes pulling the fabric body onto a machine and joining the fabric ends to form an endless belt.
A number of factors are considered when installing a dryer fabric. One factor is the time the paper machine is out of service to replace the fabric (i.e., machine downtime) including the associated cost. Another factor is the manpower required to replace a dryer fabric which can affect mill costs and operation in a number of different ways. Fabric replacement usually involves working on an overtime basis and affects (e.g., delays) other maintenance activities. It is also critical that the dryer fabric be properly installed otherwise below grade paper can result and/or additional costs can be incurred.
One important aspect of loading a fabric body onto a paper machine is that there be uniform tension across the fabric. If uniform tension is not achieved and one section of the fabric pulls more than another, then the fabric can bubble or ridge across the fabric width. Bubbling or ridging is a problem where there are small clearances, such as between blow boxes and cans, in the run of the dryer fabric through an operating machine. For example, a ridged fabric may catch in these small clearance areas and damage the fabric and/or the machine's parts (e.g., a blow box). If the fabric or machine is damaged, then the machine must be shut down, the damaged parts repaired and the damaged fabric replaced.
Another aspect of loading a fabric body is preventing damage to the fabric body seam, generally referred to as seam burnout, when removing the standard leader from the fabric body. A fabric shipped to a papermill will generally have a removable standard leader attached to facilitate loading the fabric onto the paper machine. The standard leader includes a series of grommets proximate and in a line generally parallel on one edge and at its opposite edge, it is connected to a fabric body seam by means of a wire or monofilament cable. The standard leader is later removed by pulling the wire or cable out of the seam. In order to avoid or minimize the chance of damage to the seam during installation, weight and pressures must be off the seam before pulling the wire or cable out. If the seam undergoes minor damage a wire or cable is removed, the seam may be repaired in place. However, if the seam undergoes major damage, then the damaged fabric body must be removed from the machine and another fabric body installed in its place. The damaged fabric is returned to the factory to be re-seamed so it can be used again.
A further aspect of loading a dryer fabric is properly aligning the fabric body in the machine so the dryer fabric does not wear out prematurely. If the fabric is not properly aligned in the machine during installation the fabric could oscillate during operation and/or edge curling could result.
Damaging the fabric during installation can also result in unacceptable impressions or marks in the paper produced on the fabric. In sum, improper installation may result in additional machine downtime, a need for additional manpower to correct the nonconforming condition or install a new fabric, product losses, repairs to the machine and, possibly, a damaged fabric that will have to be replaced. There is, therefore, a need for a loading harness which can reduce machine downtime and manpower requirements while assuring proper installation of the dryer fabric.
Paper mills use a variety of methods and devices for pulling dryer fabrics onto a paper machine. One of the more common devices is a loading harness made of a single ring with a number of metal cables attached thereto for connection to the dryer fabric. These cables are typically clamped to the grommets in the dryer fabric leader. Even though this is one of the quicker methods for attaching a harness to a fabric for installation, it is still time consuming. The harness must be located, moved to the site where the fabric is to be loaded onto the machine, the fabric unrolled so the harness can be attached to the standard leader, the cables untangled and finally attached to the fabric body prior to the installation process. Also, because of its metal construction, the harness is heavy and awkward to move about a mill.
As explained above, in order to avoid or minimize the potential for damaging the fabric body and the machine during installation and operation, the harness should be attached to the fabric body so there is uniform tension across the body. For the above harness, this is accomplished by having individual cables between the ring and body of different fixed lengths. This type of harness cannot automatically align and configure itself for a given application due to the fixed length metal cables. Rather, the harness must be designed and constructed to work for the particular dryer fabric to be installed.
This type of harness is very expensive to make and, as such, is not shipped with each fabric. Notwithstanding the expense, it is also unlikely that such a harness would be shipped attached to a dryer fabric because of the potential for damage to the fabric during shipping.
Using this harness also has disadvantages when removing the standard leader. Because of the ring/metal cable harness' weight and design, it is difficult and awkward to take the weight off the seam to remove the leader. As such, seam burnout is of particular concern when using this type of harness.
Another type of loading harness used in the industry is constructed from an extra length of dryer fabric which is triangular in shape and typically 20-30 feet long. This fabric harness is attached to the dryer fabric and has a grommet at the triangle's apex, opposite the dryer fabric, to pull the dryer fabric onto the machine. This type of harness is not commonly used because it is not economical to weave extra lengths of dryer fabric to make such harnesses and there is not enough of a supply of waste fabric for its production.
Another device, disclosed in U.S. Pat. No. 4,758,309, includes a supplemental strip of material mounted to and along the longitudinal edges of a fabric belt. The strip is formed with spaced apertures along the length of the belt, which apertures are shaped so that they can be gripped by hand or by a special tool. Alternatively handle loops may be attached and spaced along the length of one or both longitudinal edges presumably to be gripped by hand. This device, however, cannot be used to install dryer fabrics onto a papermaking machine for a number of reasons.
The patented device is used to install press felts which are shipped and installed as endless belts. Papermaking machines are designed so that press felts may be installed over the press section rollers from the side (i.e., installed in a direction perpendicular to the direction of travel during operation). However, paper machines are not designed to install dryer fabrics in this direction (e.g., rollers are not cantilevered so fabric can be installed from side). Thus, a dryer fabric must be pulled onto the machine parallel to the direction the fabric travels during operation.
It is also not possible to install dryer fabrics onto a paper machine by hand. The machines are not designed for access to the dryer fabric side edges to pull the fabric onto and through the machine. Therefore, the side strips or loops of this patented device would not serve any purpose. It is also not practical to install dryer fabrics by hand. Press felts are short and usually weigh 400 pounds or less, whereas dryer fabrics are typically longer and heavier. Thus as a consequence of machine design, the dryer fabric must be installed by pulling on one of the ends of the fabric body.
Moreover, use of special tools involves locating the tool at the mill, bringing it to the installation site, setting the tool up, unpacking or unrolling the fabric belt and finally interconnecting the tool in an unspecified fashion to the supplemental strip's spaced apertures prior to installation.
Therefore, it is an object of the present invention to eliminate the need to have harnesses or special tools at a paper mill for dryer fabric installation.
It is a further object of the present invention to simplify the installation process for dryer fabrics at paper mills.
It is yet another object of the present invention to provide a harness which is self-aligning to ensure uniform tension is maintained across the width of the dryer fabric.
Another object of the present invention is to provide a harness which can be attached to the fabric body before the fabric body is shipped to a paper mill.
It is yet another object of the present invention to reduce the time and costs associated with installing dryer fabrics.
It is yet a further object of the present invention to provide a harness which can be used to install seamed fabrics or seamed belts, other than dryer fabrics, onto a paper machine.